Question

In my model I have a user. The user is the athlete. A user may also be a coach to any other user. How to model this?

I have:

@user.coach? => true/false

@user.is_a_coach_of?(other_user) => true/false

Answer 1

If a user can only have one coach, then you can have a coach association on the users table back to the users table. The classic example of this is an employees table, where every employee has exactly one manager (except the CEO).

class User
  has_one :coach, :class_name => "User"
  has_many :coachees, :foreign_key => :coach_id, :class_name => "User"

  def coach?
    0 < coachees.count
  end

  def is_a_coach_of?(other_user)
    coachees.include?(other_user)
  end
end

If a user could have many coaches, then use a coaches table, with fields, user_id (for the coach) and coachee_id for the user that she coaches.

class Coach
  belongs_to :user
  belongs_to :coachee, :class_name => "User"
end

class User
  has_many coaches, :foreign_key => :coachee_id
  has_many coach_users, :through => :coachs, :source => :user
  has_many coachees, class_name => "Coach"
  has_many coachee_users, :through => :coachees, :source => :coachee

  def coach?
    0 < coachees.count
  end

  def is_a_coach_of?(other_user)
    coachee_users.include?(other_user)
  end
end